1. Field of the Invention
The present invention relates to a powder processing apparatus and powder processing system. More specifically, the present invention concerns a powder processing apparatus and powder processing system that perform spheroidization processing for improving the degree of sphericity and surface smoothness of scale-shaped powder, indefinite (polygonal) shaped powder or powder with surface irregularities, and easily pulverizable powder, and that perform compounding processing by causing the surface of powder (base powder) to be adhered by other powder (additional powder).
2. Description of the Related Art
In recent years, regarding powder used as materials for electronic techniques, materials for optical techniques, polymer materials, and medical materials, demand has grown for the improvement in the fluidity and filling property of powder by the improvement in particle shape of powder, especially by the spheroidization of its irregular-shaped particles. Furthermore, demand has also grown for the improvement in physical properties of powder, especially for the alteration of powder surfaces and the enhancement of functionality by the compounding of at least two kinds of powders. Powder processing apparatuses and powder processing systems used for such powder spheroidization processing and further compounding processing (hereinafter, these processing may be simply referred to as processing such as spheroidization) are disclosed in Japanese Examined Patent Application Publication Nos. 5-32094 and 5-32095. These apparatuses and systems are configured to include a main body portion having a cylindrical rotor and a stator arranged outside the rotor with a minute gap therebetween; a supply port provided at one end of the main body portion, and supplying powder together with an airflow along a tangential direction of the rotor; and a discharge port provided at the other end of the main body portion, and discharging powder that has been subjected to spheroidization or the like, together with the airflow along the tangential direction of the rotor.
In these powder processing apparatuses, on the outer surface of the rotor and the inner surface of the stator, a large number of protrusion members parallel to generating lines are continuously provided along a circumferential direction. Under the rotation of the rotor, a large number of minute vortexes are formed in gaps formed between individual protrusion members, and powder with irregular particle shapes, dispersed in the airflow, or at least two kinds of powders make strong contact with one another. As a result, in these apparatuses, powder is continuously subjected to processing such as spheroidization.
Furthermore, as powder processing systems, these patent documents set forth systems including, on the upstream of the powder processing apparatus, airflow generating means for generating an airflow for supplying powder to the apparatus, heat exchange means for heating and/or cooling the airflow; a raw material feeder (including a raw material mixer) for dispersing powder into the temperature-adjusted airflow, and further including, on the downstream side of the powder processing apparatus, a collector for separating from the airflow and collecting powder that has been subjected to processing such as spheroidization by the powder processing apparatus, and a blower for moving the airflow in the powder processing system.
However, in the powder processing apparatus set forth in the Japanese Examined Patent Application Publication No. 5-32094, in performing a spheroidization processing, powder that is susceptible to plastic deformation at a temperature on the level of 60° C. or less, i.e., low-melting powder could be subjected to a spheroidization processing, but powder requiring 100° C. or more for its plastic deformation, i.e., high-melting powder, and powder that is not subject to plastic deformation such as graphite could not be subjected to a spheroidization processing. With such being the situation, as a method for making the spheroidization processing implementable, increasing the revolution number of the rotor of the powder processing apparatus was thought of. However, the increase of revolution number caused strong vortexes in the gaps formed between protrusion members. This raised a problem in that powder becomes easily pulverizable and that it tends to decrease in its particle diameter, rather than it is rendered spherical.
Also in the Japanese Examined Patent Application Publication No. 5-32095, in compounding processing, when powder susceptible to pulverization was to be processed, it was necessary to prevent the powder from being pulverized by widening the gap formed between the rotor and stator, or by using an operating condition with a revolution number reduced. However, the reduction of revolution number weakened vortexes formed between the gap, thereby causing a problem of reducing the compounding effect itself. This limits the usable revolution number range and narrows the adjustment range of the compounding effect itself. Also, in order to adjust the gap, it is necessary to change the inner diameter of the stator or the outer diameter of the rotor, that is, this gap adjustment involves component replacements. This makes it difficult to freely adjust operating conditions.
It has been found that, when grooves in the axis direction of the stator in the conventional powder processing apparatus are eliminated to make a cylinder smooth, the powder can be subjected to processing such as spheroidization without being pulverized even if the revolution number of the rotor is increased. However, by this method, the progress of the processing such as spheroidization is so slow that a single pass of the powder through the apparatus does not allow the powder to be sufficiently subjected to the proceeding such as spheroidization, thus necessitating to pass the powder through the apparatus multiple times. This unfavorably makes it difficult to perform mass processing of powder. It has been further found that, in the conventional powder processing apparatus, a reduction of air volume (flow rate) to nearly one third the usual air volume allows the proceeding such as spheroidization to be promoted. However, the reduction of the air volume makes a flow of powder unstable, as well as promotes the increase in processing temperature. As a result, in powder susceptible to temperature (i.e., low-melting powder), fusion between powder particles occurs, which undesirably makes the proceeding such as spheroidization infeasible. Therefore, in order to carry out processing of powder by a single processing such as spheroidization, it is necessary to prolong the time (stay time) during which powder passes through the apparatus without reducing the air volume. In the conventional apparatuses, it might be better if the overall length of the stator and rotor are increased, but the stator and rotor have length limitations imposed by problems associated with mechanical strength, installation space, production costs or the like, resulting from the weight increase of the apparatus.